The present invention relates to a valve system for controlling flow of gas into or out of a variable volume chamber of an internal combustion engine or a compressor.
In a conventional four-stroke internal combustion engine a combustion chamber is provided by a variable volume chamber defined between a piston and a cylinder in which the piston reciprocates. Flow of fuel/air mixture into the chamber is controlled typically by a poppet valve which is spring-biassed into its valve seat. Typically a cam on a rotating camshaft engages a tappet which in turn engages the poppet valve and the opening and closing of the valve and the lift of the valve is controlled by the profile of the cam. The flow of combusted gases from the chamber is also typically controlled by an exhaust valve which is usually a poppet valve actuated by a cam on a rotating camshaft.
The use of rotating cams to control valve motion has limitations. First it is difficult to vary motion with e.g. engine speed and load, although this is preferable for increased engine efficiency. Also the need to keep valve train integrity limits the rate of opening and closing of the poppet valves. For this reason it has been proposed to connect hydraulic actuators to the poppet valves and use the hydraulic actuators to impart motion to the poppet valves. The hydraulic actuators then control the valve motion in response to control signals provided by an electronic control system. However, whilst such systems have been used on test bed engines cost have complexity and generally dictated against adoption of such valve systems in production engines. In particular the closed loop servo-valves typically used in such systems are quite expensive and can require a supply of pressurized fluid which can have high flow rates at high pressures.
The present invention provides in a first aspect a valve system for controlling flow of gas into or out of a variable volume chamber of an internal combustion engine or a compressor, the valve system comprising:
a gas flow control valve which opens to permit flow of gas into or out of the variable volume chamber;
a hydraulic actuator connected to the gas flow control valve;
a pump for pressurizing hydraulic fluid;
a reservoir of hydraulic fluid; and
a control system which controls opening and closing of the gas control valve by controlling flow of hydraulic fluid to the hydraulic actuator from the pump and flow of hydraulic fluid from the hydraulic actuator to the reservoir, the control system comprising:
an electrically controlled flow direction control valve which controls direction of flow of hydraulic fluid to the actuator to control whether the hydraulic actuator opens or closes the gas flow control valve; and
an electrically controlled switching valve which controls whether or not any hydraulic fluid flows to the hydraulic actuator and thereby controls the time of opening and closing of the gas flow control valve;
and wherein:
the pump is an electrically controlled variable flow rate pump which controls the rate of opening or closing of the gas flow control valve by controlling the rate of flow of hydraulic fluid to the hydraulic actuator; and
operation of the pump, the flow direction control valve and the switching valve is controlled by an electronic controller.
The valve system of the present invention uses separate components to carry out individual functions of the whole system. This differs from earlier proposals to provide hydraulically actuated engine valves, when typically for each engine valve a single metering servo-valve would be used to control flow rate, direction of engine valve motion and timing of opening and closing of the engine valve. The present invention allows each component to be optimized for its unique function. The overall system may be manufactured from simpler cheaper components while achieving a cheaper system which is also more efficient than previous systems.